1. Field of the Invention
The present invention relates to a speaker apparatus in which an outer periphery of a diaphragm is supported by a speaker frame through a cross-sectionally semicircular edge portion and in which an inner periphery of the diaphragm is supported by the speaker frame through what is called a corrugation damper.
2. Description of the Related Art
FIG. 1 is a longitudinally cross-sectional view illustrating a related speaker apparatus.
This speaker apparatus 1 has a magnetic circuit 3, a speaker frame 5 having a rear portion to which this magnetic circuit 3 is attached, a cone diaphragm 7 having an outer periphery to which a cross-sectionally substantially-semicircular edge portion 9 is continuously provided, a cylindrical voice coil bobbin 11 attached to an inner peripheral edge of the diaphragm 7, and a voice coil 12 wound around this voice coil bobbin 11.
The magnetic circuit 3 consists of a yoke 15 in which a cylindrical center pole 15b is provided on a disk-like plate 15a to protrude therefrom, a ring-like magnet 16 loosely fitted to an outer periphery of the center pole 15b, and a ring-like top plate 17 loosely fitted to a front end side of the center pole 15 to sandwich the magnet 16 between the plate 25a and the top plate 17. The top plate 17 is fixed to a rear end of the speaker frames.
In this magnetic circuit 3, the gap between the inner periphery of the top plate 17 and the center pole 15b is a magnetic gap in which the voice coil 12 is disposed.
The voice coil bobbin 11 fixed to the inner peripheral edge of the diaphragm 7 is connected to the speaker frame 5 through the corrugation damper 19 of a structure in which ridge and groove portions are alternately and coaxially arranged along a radial direction, thereby being hung movably in the direction of an axis of the center pole 15b. 
A mounting flange portion 9a extended from the outer peripheral rim of the outer peripheral edge member 9 connected to the diaphragm 7 is stuck to an outer peripheral portion 5a of the speaker frame 5. Thus, the diaphragm 7 is displaceably supported by the edge member 9.
That is, the diaphragm 7 has an outer peripheral portion connected to the outer peripheral portion 5a of the speaker frame 5 through the edge member 9, and also has an inner peripheral portion connected to the speaker frame 5 through a corrugation damper 19. Thus, the diaphragm 7 is elastically supported to be able to displace back and front.
It has turned out that in this speaker apparatus, the insurance of amplitude symmetry, that is, the equalization of forward and backward amplitudes of the diaphragm 7 is a major factor of suppressing occurrence of distortion of speaker sound to thereby improve sound quality.
Thus, hitherto, to ensure the amplitude symmetry, the stiffness of the edge member 9, which supports the diaphragm, and that of the corrugation damper 19 are adjusted by conditioning materials to be used.
Incidentally, in the related apparatus, usually, the edge member 9 has a cross-sectional structure in which the thickness of a cross-sectionally substantially-semicircular part thereof is uniform. However, an edge member, which is configured to have a laminated structure made of different kinds of materials to thereby obtain desired stiffness, has been proposed (See, for example JP-A-11-187481).
Further, the corrugation damper 19 is usually set, as shown in FIG. 2. That is, a bending radius Ry of the top part of the ridge portion and a bending radius Rt of the top part of the groove portion satisfy the following equation.Ry=Rt.Also, a corrugation height Hy of the ridge portion and a corrugation depth Ht of the groove portion meet the following equation.Hy=Ht.That is, the corrugation damper 19 is usually designed so that the ridge portion and the groove portion have symmetric shapes, respectively. However, a speaker apparatus, which is adapted to obtain desired stiffness by setting the corrugation heights, the corrugation depths and the bending radii R of the ridge and groove portions to vary with the outer periphery and the inner periphery, has been proposed (see, for instance, JP-A-2003-37893).